Disengageable quick-lock connection for telescopic shaft

ABSTRACT

A telescopic shaft for rapid length adjustment consists of a tube having a plurality of alternating circumferential ridges and grooves on at least a portion of an inner surface and having an oval cross-section with a major diameter D A  and a minor diameter D B ; a shaft disposed within the tube and having matching circumferential ridges and grooves, the shaft also having an oval cross-section with a major diameter D C  and a minor diameter D D ; and the ridges and grooves of the tube interengaging with the grooves and ridges of the shaft when the shaft major diameter D C  is substantially parallel with the tube minor diameter D B .

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to length-adjustable shafts andmore particularly to quick-change positive locking telescoping shafts.

[0002] There are innumerable applications in many diverse fields forlength-adjustable shafts with positive locking features. One suchapplication is in telescoping adjustable steering columns of motorvehicles, in which it is desirable to be able to quickly change thelength of the steering column and to positively lock it in the selectedposition.

[0003] Many length-adjustable shafts have quick-change capability basedon frictional locking mechanisms, similar to collets, in which a taperedring is threaded on a split tube member to frictionally lock a matingtube or shaft in position within the split tube. These are quiteeffective, but they provide clamping force which is limited by theoperator's skill in tightening the threaded ring and also by wear andcontamination of the clamping surfaces. Also, they do not providepositive locking since the clamping force can be overcome by a largeaxial load on the shaft.

[0004] Many other current shafts have rack and pawl adjustment locks inwhich a pawl is pivoted away from a rack on the sliding member of theshaft to allow change of length. When released, the pawl pivots backinto engagement with the rack by spring action to lock the shaft inposition.

[0005] Currently, still other such shafts are made by threading theinside of a tube and the outside of a mating shaft and then axiallycutting away slightly more than half the threads on both members bymachining flats on opposing sides of the shaft and arced grooves onopposing sides of the inside of the tube. The shaft can then be insertedin the tube with its remaining threads aligned with the arced grooves ofthe tube so it slides into the desired position. The shaft is given aquarter turn to lock it in any position relative to the tube. Toreadjust the length of the shaft/tube couple, it is only necessary toturn either member one-quarter turn and slide it to the new position andre-lock it. These provide quick adjustment and are capable of positivelocking, but the presence of burrs at the edges of the machined flatsand grooves often prevents turning the tube and shaft to the lockedposition. Even without burrs, the flats at the edges of the threads onthe shaft and tube may butt against each other and prevent turning tothe locked position; because they have no normal lead in as would befound in common threads.

[0006] The foregoing illustrates limitations known to exist in presentquick-change adjustable length shafts. Thus, it would clearly beadvantageous to provide an alternative directed to overcoming one ormore of the limitations set forth above. Accordingly, a suitablealternative is provided including features more fully disclosedhereinafter.

SUMMARY OF THE INVENTION

[0007] In one aspect of the present invention, this is accomplished byproviding a telescopic shaft for rapid length adjustment, comprising atube having a plurality of substantially circumferential alternatingridges and grooves on at least a portion of an inner surface and havingan oval cross-section with a major diameter D_(A) and a minor diameterD_(B); an inner shaft member disposed within said tube and havingmatching ridges and grooves, the shaft also having an oval cross-sectionwith a major diameter D_(C) and a minor diameter D_(D); and the ridgesand grooves of said tube interengaging with the grooves and ridges ofsaid shaft when the shaft major diameter D_(C) is substantially parallelwith the tube minor diameter D_(B).

[0008] The foregoing and other aspects will become apparent from thefollowing detailed description of the invention when considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIGS. 1a, 1 b, and 1 c are three transverse sectional views of atelescopic shaft of the invention;

[0010]FIG. 2 is a fragmentary longitudinal partly sectional explodedview of the telescopic shaft; and

[0011]FIGS. 3a and 3 b are fragmentary perspective views of analternative embodiment of the inner shaft member and a longitudinalsection of the matching outer tube member, respectively.

DETAILED DESCRIPTION

[0012]FIGS. 1a, 1 b, and 1 c show transverse sectional views of thetelescopic shaft 100 of the invention. For best understanding of thefeatures of the invention, it is best to consider FIGS. 1, 2, and 3, asappropriate, in order to see longitudinal and perspective views whennecessary. In its simplest form, the telescopic shaft 100 consists of anouter tube member 10 and an axially slidable inner shaft member 20, eachof which have oval cross-sections and alternating circumferentialgrooves and ridges (See FIG. 2) or, alternatively, continuous threads ontheir contacting surfaces. The outer tube member 10 has a major diameterD_(A) and a minor diameter D_(B). The inner shaft member 20, disposedwithin the outer tube 10, has matching ridges and grooves and also hasan oval cross-section with a major diameter D_(C) and a minor diameterD_(D).

[0013]FIG. 1a shows the major diameters D_(A) of the outer tube member10 and D_(C) of the inner shaft member 20 in parallel relationship. Inthis position the inner shaft member 20 can slide axially within theouter tube member 10. FIG. 1b shows the major diameter D_(C) of theinner shaft 20 rotated to a position, approaching the minor diameterD_(B) of the outer tube 10, in which its grooves 27 and ridges 25 beginto interengage with the ridges 15 and grooves 17 of the tube 10.

[0014]FIG. 1c shows the outer tube and inner shaft in the fully lockedposition in which the major diameters are at right angles to each other.Here the ridges 15 of the tube are maximally engaged with the grooves 27of the shaft, and the ridges 25 of the shaft are maximally engaged withthe grooves 15 of the tube. Of course, even though there is a largedifference in the diameters of the tube and shaft, the alternatingridges 15 and grooves 17 of the outer tube 10 may tend to engage thealternating grooves 27 and ridges 25 of the inner shaft 20, merely dueto the difficulty of keeping a long shaft centered in a long tube, andmake it difficult to slide one relative to the other. To prevent anyunwanted engagement, a centering plug 30 may be pivotally mounted on theend of the shaft 20 on a pin or journal 35. This plug 30 has a slip fitin the outer tube 10 so that it is easily moved, but it just clears theridges of the tube. The plug 30 keeps the inner shaft 20 properlycentered in the outer tube 10, so there is no unwanted engagementbetween the ridges and grooves of the members when the shaft is beingtelescopically adjusted. Of course, when the ridges and grooves of theinner and outer members are prevented from engagement by other means,the centering plug is not needed.

[0015]FIG. 2 shows a fragmentary partially sectional longitudinalexploded view of the telescopic shaft of the invention as shown in FIG.1c. In this view, the ridges 15 and grooves 17 of the tube 10 and themating grooves 27 and ridges 25 of the shaft 20 are seen in their lockedconfiguration with their major diameters crossed at right angles to eachother. (D_(B) is parallel to D_(C)). The centering plug 30 is rotatablyattached to the end of the shaft 20 by a spindle or other fastener 35,so that, when the major diameters of the shaft and tube are parallel, asin FIG. 1a, the plug 30 keeps the grooves and ridges of the shaft 20separated from the ridges and grooves of the tube 10. This centeringaction allows smooth and easy length adjustment. The shaft may be madefrom a heavy-walled tube (not shown) to save weight. In that case, theplug fastener would need to provide adaptation for fastening thecentering plug to the shaft by any of several well known options.

[0016]FIGS. 3a and 3 b show an alternative embodiment of the inner shaftmember 50 and the outer tube member 40. In this embodiment, the ridges55, 45 and grooves 57, 47 are provided only on the portions of the outertube 40 and inner shaft 50 which actually interengage when locked. Theends 42 of the outer member 40 in line with the major diameter and thesides 52 of the inner member 50 in line with its minor diameter need nothave any ridges and grooves. Thus, the ridges and grooves only appear onthe surfaces of the shaft and tube in line with the major diameter ofthe shaft and the minor diameter of the tube. It is clear from theseFIGS. that the inner shaft 50 need not be oval, as shown in FIG. 3A. Thesides 52 can be flat so that the shaft has a double D profile as long asit has ridges 55 and grooves 57 at its ends to interengage with grooves47 and ridges 45 on the sides of the outer tube 40. The shapes of theinner and outer members can be any which have congruent arcuatecross-sections on which the ridges and grooves are disposed.

[0017] The methods for making the invention include fully threading theID of a tube and the OD of a shaft and deforming them both until themajor diameter of the shaft is approximately equal to the minor diameterof the tube. The ridges and grooves can be made as separate parallelcircumferential forms or a continuous thread. The threads, oralternating grooves and ridges, may be formed by cutting or machiningprocesses, or they may also be formed by rolling or other non-cuttingtechniques. This would be determined by the equipment available.

[0018] Another method for making the telescopic shaft requires procuringa tube with an oval cross-section and a shaft, which may be hollow, alsowith an oval cross-section. A circular threading tool, cutting tool, orrolling tool is used to form alternating grooves and ridges on the shaftand tube in line with the major diameter of the former and the minordiameter of the latter. This would have the advantage of minimizing theamount of starting material needed. It would also minimize waste byminimizing the amount of cutting necessary to provide the ridges andgrooves on the shaft and tube, in cases where the cutting method ischosen for forming the ridges and grooves.

[0019] In order to prevent turning the shaft or tube through a greaterarc than necessary for locking the telescopic shaft length, it would bepossible to make the major diameter D_(C) of the shaft 20 slightlygreater than the minor diameter D_(B) of the tube 10. This would preventturning the shaft past the locked position back to an unlocked position,but it could cause jamming of the engaging ridges and grooves if turnedtoo tightly. Another solution is to include an axial key or otherdiscontinuity in the alternating ridges and grooves. The discontinuitycan be provided by any axial interruption in the alternating ridges andgrooves such as a weld bead or a rolled groove to disrupt the smoothgroove/ridge profile. This discontinuity can be provided on either oneor both of the members. Since it does not require any additionalmanufacturing steps, the first option, that of providing a shaft majordiameter greater than the tube minor diameter, is preferred.

Having described the invention, we claim:
 1. A telescopic shaft forrapid length adjustment, comprising: a tube having a plurality ofsubstantially circumferential alternating ridges and grooves on at leasta portion of its inner surface and having an oval cross-section with aninside major diameter D_(A) and minor diameter D_(B); an inner shaftmember disposed within said tube and having matching ridges and grooves,said inner shaft member also having an oval cross-section with a majordiameter D_(C) and a minor diameter D_(D); and the ridges and grooves ofsaid tube interengaging with the grooves and ridges of said inner shaftwhen the shaft major diameter D_(C) is substantially parallel with thetube minor diameter D_(B).
 2. The telescopic shaft of claim 1 , furthercomprising: means for limiting rotation of said inner shaft memberwithin said tube.
 3. The telescopic shaft of claim 2 , wherein the meansfor limiting rotation of said inner shaft member within said tubecomprises said inner shaft major diameter D_(C) being slightly greaterthan said tube minor diameter D_(B), such that said inner shaft islimited to slightly less than 180° of rotation within said tube and saidridges and grooves are fully interengaged at the limits of rotation. 4.The telescopic shaft of claim 1 , wherein the circumferentialalternating ridges and grooves comprise a continuous thread.
 5. Thetelescopic shaft of claim 1 , further comprising: a centering plughaving an oval cross-section and a slip fit in the tube, said plug beingrotatably attached to the end of the inner shaft member for radiallycentering said shaft member within said tube.
 6. The telescopic shaft ofclaim 2 , wherein the means for limiting rotation of said inner shaftmember within said tube comprises at least one axial discontinuity inthe ridges and grooves of the tube to act as a stop against furtherrotation when the inner shaft has been rotated to the locked position inthe tube.
 7. A method for making a quick-change length-adjustabletelescopic shaft, comprising the following steps: providing an outertube member having an oval cross-section with an inside major diameterD_(A) and minor diameter D_(B); forming a plurality of substantiallycircumferential alternating ridges and grooves on at least a portion ofthe inner surface of said outer tube member; providing an inner shaftmember having an oval cross section with a major diameter D_(C) and aminor diameter D_(D); forming a plurality of substantiallycircumferential alternating ridges and grooves on at least a portion ofthe outer surface of said inner shaft member.
 8. The method of claim 7 ,comprising the further step of: rotatably attaching a centering plug tothe end of the inner shaft member for radially centering said innershaft member within said outer tube member.
 9. The method of claim 7 ,comprising the further step of: forming at least one axial discontinuityin the ridges and grooves of the outer tube member to act as a rotationstop when the inner shaft member has been rotated to the locked positionin the outer tube member.
 10. A method for making a quick-changelength-adjustable telescopic shaft, comprising the following steps:providing an outer tube member; deforming said outer tube member toprovide an oval cross-section with an inside major diameter and minordiameter; providing a hollow inner shaft member; deforming said innershaft member to provide a continuous oval cross-section with an outsidemajor diameter and minor diameter, the major diameter of said innershaft being equal to the minor diameter of the outer tube; and forming aplurality of matching alternating circumferential ridges and grooves onat least a portion of the inside surface of the outer tube member andthe outside surface of the inner shaft member.